We have a serial killer who is killing people in a serialistic fashion. But, it turns out that everyone he is killing is actually also a mascot person. And, it turns out that they each are animal mascots.

Our protagonist detective and his partner find this out somehow, but they can't tell which mascot person is going to be next. No pattern, see?

But, in fact, there is a pattern. And, if they only knew it, they could catch the killer guy.